Numerical study on the chemical reaction kinetics of n-heptane for HCCI combustion process

The combustion mechanism of n-heptane have been investigated using a zero-dimensional thermodynamic model coupled with a detailed kinetic model. At low temperature reaction, the main initial reactions are NC7H16 + O2 = C7H15-2 + HO2 and NC7H16 + O2 = C7H15-3 + HO2. H-atom abstraction from n-heptane occurs primarily by OH and HO2. The first O2 addition and the second O2 addition are the most important paths for the low temperature branching. High temperature reaction includes two stages: blue-flame reaction and hot-flame reaction. Blue-flame reaction which is controlled by H2O2 decomposition is mainly the process of the conversion of CH2O to CO by reactions CH2O + OH = HCO + H2O and HCO + O2 = CO + HO2. Hot-flame reaction which is dominated by reaction H + O2 = O + OH is mainly the process of the oxidization of CO to CO2 by reaction CO + OH = CO2 + H. There are four regions for HCCI combustion including: I complete combustion region; II high CO emissions region where low-temperature reaction and blue-flame reaction occur; III high CH2O emissions region where only low-temperature reaction occurs and IV misfire region.